This invention relates generally to sulfurized olefins useful as EP additives in lubricating oils and more specifically to a two-stage process for making sulfurized olefins having improved oil solubility in which a first stage adduct of olefin and sulfur monochloride having a 1.7 to 1.9:1 mole ratio of olefin to sulfur monochloride is formed at controlled low temperatures and then reacted with sodium sulfide.
Sulfurized olefins are well-known additives for use in lubricating oils. One method of preparing such materials involves a two-stage reaction process where in the first stage the olefin, such as isobutylene, is added to sulfur monochloride to form an adduct The reaction is exothermic and is usually carried out at temperatures of 20.degree.-80.degree. C. and preferably between about 50.degree.-60.degree. C. In practice, the olefin is added until the reaction stops as indicated by the loss of exotherm. Preferred amounts of from about 1.5 to 2.2 gram moles of olefin per mole of sulfur monochloride have been disclosed but the reaction is self-limiting due to the loss of HCl from the product and a typical self-limiting ratio is about 1.7 to 1. The first stage adduct is then reacted with sodium sulfide and sulfur in an aqueous, alkanol reaction medium at temperatures of from about 50.degree. C. up to reflux. The resulting products are useful EP additives which are soluble in mineral oils but not in hydrotreated oils. The preparation of organic polysulfides from adducts made by reacting an olefin having from at least six to about 30 carbon atoms with about a stoichiometric equivalent of a sulfur halide at a temperature of from about 0.degree. C. to 50.degree. C. is disclosed in U.S. Pat. No. 2,708,199. We have now discovered a novel, low temperature process for preparing hydrotreated oil soluble, sulfurized olefins.